jpeg(3tcl)						      JPEG image manipulation							jpeg(3tcl)

__________________________________________________________________________________________________________________________________________________

NAME

       jpeg - JPEG querying and manipulation of meta data

SYNOPSIS

       package require Tcl  8.2

       package require jpeg  ?0.4.0?

       ::jpeg::isJPEG file

       ::jpeg::imageInfo file

       ::jpeg::dimensions file

       ::jpeg::getThumbnail file

       ::jpeg::getExif file ?section?

       ::jpeg::getExifFromChannel channel ?section?

       ::jpeg::formatExif keys

       ::jpeg::exifKeys

       ::jpeg::removeExif file

       ::jpeg::stripJPEG file

       ::jpeg::getComments file

       ::jpeg::addComment file text...

       ::jpeg::removeComments file

       ::jpeg::replaceComment file text

       ::jpeg::debug file

       ::jpeg::markers channel

_________________________________________________________________

DESCRIPTION

       This  package  provides commands to query and modify JPEG images. JPEG stands for Joint Photography Experts Group and is a standard for the
       lossy compression of photographical images. It is specified at LINK_HERE.

COMMANDS

       ::jpeg::isJPEG file
	      Returns a boolean value indicating if file is a JPEG image.

       ::jpeg::imageInfo file
	      Returns a dictionary with keys version, units, xdensity, ydensity, xthumb, and ythumb. The values are the associated  properties	of
	      the JPEG image in file.  Throws an error if file is not a JPEG image.

       ::jpeg::dimensions file
	      Returns the dimensions of the JPEG file as a list of the horizontal and vertical pixel count.  Throws an error if file is not a JPEG
	      image.

       ::jpeg::getThumbnail file
	      This procedure will return the binary thumbnail image data, if a JPEG thumbnail is included in file, and the empty string otherwise.
	      Note  that it is possible to include thumbnails in formats other than JPEG although that is not common. The command finds thumbnails
	      that are encoded in either the JFXX or EXIF segments of the JPEG information. If both are  present  the  EXIF  thumbnail	will  take
	      precedence.  Throws an error if file is not a JPEG image.

		  set fh [open thumbnail.jpg w+]
		  fconfigure $fh -translation binary -encoding binary
		  puts -nonewline $fh [::jpeg::getThumbnail photo.jpg]
		  close $fh

       ::jpeg::getExif file ?section?
	      section must be one of main or thumbnail.  The default is main.  Returns a dictionary containing the EXIF information for the speci-
	      fied section.  For example:

		  set exif {
		Make	 Canon
		Model	 {Canon DIGITAL IXUS}
		DateTime {2001:06:09 15:17:32}
		  }

	      Throws an error if file is not a JPEG image.

       ::jpeg::getExifFromChannel channel ?section?
	      This command is as per ::jpeg::getExif except that it uses a previously opened channel.  channel should be a  seekable  channel  and
	      section  is  as described in the documentation of ::jpeg::getExif Note: the jpeg parser expects that the start of the channel is the
	      start of the image data. If working with an image embedded in a container file format it may be necessary to read the jpeg data into
	      a temporary container: either a temporary file or a memory channel.

       ::jpeg::formatExif keys
	      Takes a list of key-value pairs as returned by getExif and formats many of the values into a more human readable form. As few as one
	      key-value may be passed in, the entire exif is not required.

		  foreach {key val} [::jpeg::formatExif [::jpeg::getExif photo.jpg]] {
		      puts "$key: $val"
		  }

		  array set exif [::jpeg::getExif photo.jpg]
		  puts "max f-stop: [::jpeg::formatExif [list MaxAperture $exif(MaxAperture)]]

       ::jpeg::exifKeys
	      Returns a list of the EXIF keys which are currently understood.  There may be keys present in getExif data that are not  understood.
	      Those keys will appear in a 4 digit hexadecimal format.

       ::jpeg::removeExif file
	      Removes  the Exif data segment from the specified file and replaces it with a standard JFIF segment.  Throws an error if file is not
	      a JPEG image.

       ::jpeg::stripJPEG file
	      Removes all metadata from the JPEG file leaving only the image. This includes comments, EXIF segments, JFXX segments,  and  applica-
	      tion specific segments.  Throws an error if file is not a JPEG image.

       ::jpeg::getComments file
	      Returns a list containing all the JPEG comments found in the file.  Throws an error if file is not a valid JPEG image.

       ::jpeg::addComment file text...
	      Adds one or more plain text comments to the JPEG image in file.  Throws an error if file is not a valid JPEG image.

       ::jpeg::removeComments file
	      Removes all comments from the file specified.  Throws an error if file is not a valid JPEG image.

       ::jpeg::replaceComment file text
	      Replaces	the first comment in the file with the new text.  This is merely a shortcut for ::jpeg::removeComments and ::jpeg::addCom-
	      ment Throws an error if file is not a valid JPEG image.

       ::jpeg::debug file
	      Prints everything we know about the given file in a nice format.

       ::jpeg::markers channel
	      This is an internal helper command, we document it for use by advanced users of the package. The argument channel is  an	open  file
	      handle  positioned  at  the  start  of the first marker (usually 2 bytes). The command returns a list with one element for each JFIF
	      marker found in the file. Each element consists of a list of the marker name, its offset in the file, and  its  length.  The  offset
	      points to the beginning of the sections data, not the marker itself.  The length is the length of the data from the offset listed to
	      the start of the next marker.

LIMITATIONS

       can only work with files cant write exif data gps exif data not parsed makernote data not yet implemented

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain bugs and other problems.  Please report such in the category jpeg	of
       the  Tcllib  SF	Trackers [http://sourceforge.net/tracker/?group_id=12883].  Please also report any ideas for enhancements you may have for
       either package and/or documentation.

KEYWORDS

       comment, exif, image, jfif, jpeg, thumbnail

CATEGORY

       File formats

COPYRIGHT

       Copyright (c) 2004-2005, Code: Aaron Faupell <afaupell@users.sourceforge.net>
       Copyright (c) 2007, Code:  Andreas Kupries <andreas_kupries@users.sourceforge.net>
       Copyright (c) 2004-2009, Doc:  Andreas Kupries <andreas_kupries@users.sourceforge.net>
       Copyright (c) 2011, Code: Pat Thoyts <patthoyts@users.sourceforge.net>

jpeg								       0.4.0								jpeg(3tcl)